﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace System
{

    public static class SystemExtensions
    {

        public static bool IsPhoneNumber(this string phoneNumber)
        {
            return !string.IsNullOrEmpty(phoneNumber) && phoneNumber.Length == 11 && phoneNumber.StartsWith("1");
        }

    }

}